Process and apparatus for producing wood pulp



C. B. THORNE Filed April 5, 1925 PROCESS AND APPARATUS FOR PHODUCING WOOD PULP Nov. 13, 1928.

lPatented Nov. 13, 1928. u

UNITED STATES PATENT oFFlca PROCESS AND APPARATUS FOR PRODUCNG WOOD PLP.

Application led April 5, 1926. Serial No. 99,914.

My invention relates to the cooking of cellu` losi material to produce pulp and more particularly to the heating andmovement of the liquor` used in such cooking.

It is well known in the art that Wood in the desired form may be cooked in a digester with different types of liquor, to free the Wood from its encrusting materials and liberate the fibre and my process is applicable to the use of any of the usual cooking liquors. Dilliculty has beenencouutered in providing apparatus which Will withstand the corrosive -eiects of various cooking liquors and large quantities of steam are required for maintaining the required cooking temperatures as Well as for the circulation of the liquor and pulp.

It is an object of my invention to provide a novel process and means for moving or circulating the cooking liquor.

A further object of my invention is to provide a process and means for supplying the digester, lled With Wood, With a liquor. at substantially the required cooking temperature and pressure.

A still further object of my invention is to utilize vthe heat contained in the waste gases and liquor, incident to the operation of the process, fori preheating the cooking liquor.

Further objects of my invention arev to shorten the time required for cooking the Wood; to reduce the amount of liquor re'- quired; to obtain a thorough circulation of the cooking liquor; to produce a uniform qual-ity of pulp for the manufacture of paper,

`silk and other articles of commerce, to obtain a high yield from the digester and generally. to provide an improved, easily controlled process for economically cooking Wood, all of which will appear from the detailed description now to be given.

While, as previously stated, my process and apparatus may be used With any cooking li uor, I shall describe it With particular reqference to the so-called sulphite process. Tn this process itv is particularly desirable to retain the SO2 gas in the liquor. When the liuor is heatedthere is a tendency for the l S 2 to be liberated and to avoid this T maintain the heated liquor, under a pressure. This I accomplish by the' use of a gas, which may be circulated as desired through the ap-- paratus, as will hereinafter appear. Any 'desired gas may be used, which Will not form undersirable reactions with the liquor. In

this'particular operation of the process SO2 gas 1s very effective. I have also used nitrogen, but any suitable gas may be employed.

The accompanying drawing illustrates diagrammatically and by Way of example one form ofthe apparatus of my invention as used for the operation of the process.

The tank 1 is an ordinary storage tank for the supply of cooking liquor and it is connected through the pump 2 to a series of heaters 3, 3b, 3, a valve 4 being provided to regulate. the discharge from the tank. The heaters are provided with heating coils 5. The pipe 6 is provided With a check valve 7 and leads to a ho-t liquor tank 8, which is connected to a circulating or pulsating tank 9 by meansof pipes 10 and 11 having valves 12 and 13. This tank 9 is connected by means of an extension of pipe 11,'having valve 14, through a heater v15 to the cooking liquor line 16 which as indicated leads to a series of digesters 17 a and 17 b. Only two such digesters are shown but any desired number maybe used. The pipe 18a, having a valve 19a, leads from the liquor line 16 to the top of the digester 17 a and the pipe 18b having the valve 19h leads to the top of the digester 17h, WhileA and 28d, having valves 29a, 29", 29,c and .29d

respectively, to the hot liquor tank, the pulsating or circulating tank 9 and the digesters 17a and 17 b respectively. A pipe 30having a safety valve 31 leads from the compressed gas tank 24 to the tank 22. A gas relief line 32, having a safety valve 33', is connected to the hot liquor tank 8, the pulsating tank 9 and the digesters 17a and 17b respectively by means of the pipes 34a, 34h, 34 and 34d having valves 35a, 35h, 35c-and 35d respec` tively. This gas relief line 32 conveys the relief gases to the heaters and or to a gas recovery device. f A pipe 36 having a stop valve 37 and a safety valve 38 connects the tank 8 with the gas supply tank 22.

The digesters are of the-usual construction and when required are lined with a material resistant to the ac-ion oftheV cooking liquor used. The liqpor ank 8 and the circulating tank 9 are of similar construclikewise resistant to the action capable of withwork-I or pulsating tion and are of the liquor employed and standin the pressures incident to the ing of t ie-process.

The heaters 3, 3b and 3 are made of or lined with a material resistant to the action of the cooking liquor. Any desiredvnumber of heaters may be employed and they may be heated in any desired Way, but in accordance with my invention, I prefer to utilize the heat from the waste products of the process for this purpose. Thus the hot waste liquors from the blow pit, well known in the artand consequently not shown in the drawing, may be passed through the coil 5 in the heater 3, While the relief products from the digesters may be passed through the coil 5 in heater 3b and live steam, a hot gas or fluid or even a .lirect flame may bel used for heating the heater 3, to finally bring the temperature of the liquor passing therethrough to the required temperature. If desired the liquor may be circulated through the coils 5 and the heating medium about them. In anycase,

when spent liquors are used as the heating medium, I maintain the pressure of the heating medium higher than that of the liquor, passing through the heaters, so that should leaks occur the fresh liquor will not esca-pe into the heating medium.

A Moreover, an additional heating element, not shown, may be placed in tank 8 to further assist in raising the temperature of the liquor. The heater 15 may be of any desired type and may have a heating coil 15 therein.

The pump 2 is designed to be adapted to fill the hot liquor tank 8 against a pressure of approximately 100 lbs. as in accordance wlth my invention, a constant pressure is maintained on the liquor in this tank. The safety valves are designed to maintain a predetermined desired pressure in the respece tive parts of the apparatus. The operation of my/process and apparatus is as follows:

By means of the compressor 23 gas from the supply tank 22 is forced into the compressed gas supply tank 24, from which it 1s passed through pipes 27 'and 28l into the hot liquor tank 8, until a pressure of approximately 7 0 lbs. is produced therein, when valve 29 is closed. The valve 37 being open the safety valve 38 maintains a constant pressure in tank 8. l K

Liquor is pumped from the liquor supply tank 1 through the heaters 3, 3b and 3 where it is heated to a temperature of 100"-l30o C. more or less, depending on thel pressures employed, into the tank 8 under pressure, while the gas is relieved through pipe 36 and safety valve 38 into thegas supply tank 22. When the tank 8 is substantially filled vthe valve 4 is closed and the ump 2 stopped.

The digester 17a having een filled with chips in the usual manner, valve 29 is opened an gas is allowed to pass intothe digester isreached, depending upon the cooking pressure employed, when valve 29 `is closed. Valves 12,14, 21, 29L and 35 are opened, and valve 35 being closed hot liquor is forced into the digester from thevbottom,vwhile the gas from the digester is relieved through pipe 34, the relief line 32 and safety valve 33. rThis movement of the liquor is vcaused by the pressure of the gas on the liquor in tank 8. If it is desired to fill the digester from the top, it will be apparent that valve 19a would be opened instead of valve 21 or the liquor may be run into the digester from both top and bottom by opening both these valves. When the digester is filled with liquor the valves 21 and or 19, 14, 12 and 29 are closed and if it is necessary to further raise' the temperature steam may be admitted to the digester in the usual manner.

It will be apparent that, inasmuch as the until a pressure of substantially -100 lbs.

liquor is introduced into the digester ata v Valve 29b is opened to allow gas to iiow from the tank 24 to the circulating or pulsating tank 9 until the pressure therein becomes substantially equal to that in the digester, when valve 29b is closed. Valves 29, 21, 14 and 13 are opened and gas from the compression tank 24 flows into the digester forcing the liquor out into the tank 9, while at the same time valve 35b is opened to permit the relief of the gas from tank 9. When the desired amount of liquor has been withdrawn from the digester valves 35, 29 and 21a are closed and valves 19, 35 and 29b are opened and the liquor from the tank 9 is forced into the top of the digester. If desired the liquor may be forced directly back into the bottom of the digester, thus causing what I term, 4

a pulsation in the'digester, instead .of the straight circulation of the liquor. This circulating or pulsating operation is repeated as often as desired in connection with the particular material being treated. Obviously while I have shown the liquor' as being removed from the bottom of thedigester, it may be Withdrawn at any desired. point.

The cooking operation may thus becompleted or I may proceed. as hereinafter described.4

Thus far I have not described the operation of the digester 17b or other members of thel series'of digesters. which I may emplby,

but it will be apparent that they may be the temperature of the cooking liquor, thus employed in the same manner as digester 17 just described, each digester operating as an independent unit.

In the treatment of some classes of wood it may be preferable to operate the digesters successively l or in conjunction one with another and my invention comprehends such method of operation. Thus afterthe charge .of chips in digester 1'?a has been cooked for a period of time, as above described, I may transfer the liquor from this digester to digester 17h, which has previously been filled with chips and has a gaspressure of about 7 0 lbs. therein, by opening valves 29, 2l, 2lb' and 35d. When the 4liquor is transferred from digester 17a to digester 17", these valves are closed and if necessary steam is admitted to digester 17b and the cook progresses therein. A further charge of fresh liquor from tank 8, of used liquor from one-of the digesters of the series, or even of liquor from a source, not shown, is then forced into digester 17 -to complete the cooking of the charge.. I .also contemplate the treatment of the chips inthe digester with more than the two treating liquors speciiically mentioned and such liquors will be transferredl as required by means of the gas under pressure as previously described. The completely cooked charge is finally transferred to the blow pit in the usual manner.

While I may admit steam directly to the cooking liquor to raise its temperature, it will be understood that I prefer to employ indirect heating to avoid the dilution of the liquor.

I have not shown in the drawings means for maintaining a higher pressure in the heating medium flowing through the heaters, than that of the liquor being heated, as those skilled in the art may readily providesuch means. For example, a pump may be employed to raise the pressure of the waste liq.

uor, coming from the digester to the heater coils, to the required point and pressure valves to maintain V.such pressure in the coils at all times. Should the pump through accident or other cause be shut down such valves would be designed to maintain the predetermined pressure in the coils and thus prevent the loss of liquor, as previously described. y

It will be understood that the term wood used in the specification and claims includes any cellulosic material from which pulp may be made. f

It will thus be apparent that in accordance with my process a hot cooking liquor is applied directly to the chips under a sustained presure and that such liquor is caused to circulate or pulsate in the digester, without the use of a pump or other moving mechanical part-s coming into contact with the hot liquor. The heat contained in'the waste gases and liquor ordinarily lost, is utilized to raise reducing the amount of fuel consumed in the cooking of the wood. The additional advantages of my process will be apparent to those skilled in the art.

Having now particularly described my invention, what I claim is-:-

l. A process of preparing wood pulp which comprises injecting a preheated liquor into wood chips in a digester against a subst-anti'ally constant pressure derived from an external gas and causing a circulation of said liquor in the digester, pressure for said cirf culation being derived from said external gas.

2. A process of prepa-ring wood pulp which comprises forcing a preheated liquor into a digester containing Wood chips under pressure, by means of an external body of gas under pressure, so that the dig-ester ischarged at substantially cooking temperature and pressure, and cooking the chips therein.

3. A process of cooking wood which consists in preheating a cooking liquor by'utilizing heat of waste products of the process, admitting said preheated liquor to a charge of Wood chips under a pressure in a digester, said pressure bein derivedfrom an external gas, cooking the c ips with said liquor and periodically causing the liquor to circulate or pulsate in the digester, pressure for said circulation or pulsation being derived from said external gas.

4. A process of cooking wood which coma preheated liquor and at a cooking temperature, withdrawing liquor fromathe bottom of the digester to a circulating or pulsating tank and returning said liquor to the bottom of the digester, the hot liquor being under pressure throughout the operation of the process and the movement of the liquor being effected by a body of gas under pressure.

5. In a process of cookin wood, heating the cooking liquor, charging 1t into a digester containing wood chips, circulating yor pulsating it in the digester. and keeping said liquor under a predetermined substantially constant pressure throughout the process.

6. In a process of cooking wood chips with liquor, in a digester, the step which consists in moving the liquor from and to the digester with an external body of gas under pressure.

7. In a process of cooking woodvchips with a preheated liquor4 in a digester, the step which consists in maintaining said liquor the' container or the digester from which the liquors are to be transferred.

ternal source of independent gas to supply gas under pressure to circulate liquor from and to said tank to and from said digester and means for the release of said gas from the di- .gester and tank as each is being charged with liquor.

- 11. An apparat-us for cooking wood chips comprising a digester, a liquor tank, a liquor circulating or pulsating tank, and an external source of independent gas to supply gas under pressure to maintain liquor in said apparatus under a predetermined pressure and to circulate said liquor in the apparatus.

12. An apparatus for cooking wood chips comprising a digester, a liquor circulating or pulsating tank with connections to the upper and lower portions of said digester, a compressed external gas supply receptacle hav-v ing connections with'said. digester and tank 'adapted to admit compressed gas thereto for the purpose of circulating liquor therein and means adapted tov permit the relief of gas from said digester arid said tank at a predetermined pressure.

13. An apparatus for cooking wood chips -comprising in combinat-ionvheaters adapted to preheat liquor, a` hot liquor tank, a digester, a liquor circulating tank, valve controlled connections bet-weenthe top and bottom of said digesterand said tanks, connections between said tanks, the digester and a compressed (ras supply receptacle and means to control the flow of compressed gas through said last named connections, to permit t e flow of liquorI between said tanks and said digester under a predetermined pressure.

14. An apparatus as defined in claim 1l having an auxiliary liquor heater located between said liquor circulating tank and said digester.

15. An apparatus for cooking wood chips having in combinationy with a digester and liquor supply and circulating tanks, a compressed gas receptacle and connections adapted to permit the regulated flow of compressed gas to cause the circulation of liquor under a predetermined pressure.

16. An apparatus for cooking Wood chips comprising, a series of digesters in combination With liquor heaters, a liquor tank, a liquor circulating or pulsating tank and means adapted to circulate a gas under pressure to effect the transfer of liquor'in said apparatus in acontrolled manner and to maintain a predetermined pressure in said apparatus. Y

In testimony whereof I aiiix m signature.

CARL BUSCH 'r ORNE. 

